1. Field of the Invention
The present invention relates to a hydrocarbon reforming catalyst, and more particularly, to a catalyst comprising ruthenium and zirconium employed in hydrocarbon reforming making use of carbon dioxide; a method for producing the catalyst; and a method for reforming hydrocarbon by use thereof. The present invention also relates to an autothermal reforming catalyst comprising ruthenium and zirconium; a method for producing the catalyst; and a method for producing hydrogen or a synthesis gas by use of the catalyst.
2. Background Art
A variety of techniques are known for producing a synthesis gas and hydrogen through reforming of organic compounds such as hydrocarbon. Particularly, many steam reforming techniques have been brought into practice for reforming hydrocarbon by use of steam. In these techniques, principally, hydrogen or a synthesis gas for producing methanol is produced from a starting material such as methane, LPG, or naphtha by use of a nickel catalyst.
In general, reforming of hydrocarbon through steam reforming involves a large-scale endothermic reaction. Therefore, when steam reforming is carried out on an industrial scale, heat supply from the outside raises a technical problem which must be solved. Particularly, the overall reaction of industrially-employed steam reforming of hydrocarbon by use of a nickel catalyst is considerably endothermic at 600xc2x0 C.-900xc2x0 C. For example, the overall reaction of steam reforming of methane is endothermic, with a heat of reaction of 49.3 kcal/mol at about 700xc2x0 C. Although various attempts have been made toward improving a reactor and a heat recovery system, such improvements do not represent essential solutions for attaining enhanced heat recovery and simplified facilities.
Another known technique for producing a synthesis gas and hydrogen is partial oxidization of hydrocarbon. A technique for producing a synthesis gas and hydrogen by partially oxidizing heavy hydrocarbon, such as vacuum residue, with oxygen at high temperature has already been brought into practice. In addition, Japanese Patent Application Laid-Open (kokai) No. 05-221602 discloses a method for producing a synthesis gas, in which partial oxidation of methane is performed at a temperature nearly equal to that of steam reforming making use of a catalyst comprising zirconium and ruthenium. In this case, heat of oxidation is problematic in that it must be removed. Reforming through partial oxidation requires further studies, in view of stability of reaction and saving energy.
In view of the foregoing, there has been investigated autothermal reforming, in which a starting material for producing a synthesis gas such as hydrocarbon is partially oxidized and simultaneously reformed by use of a reforming gas such as steam, so as to balance heat of reaction.
Conventionally, there has been investigated application of catalysts such as a nickel catalyst, a platinum catalyst, or a palladium catalyst to autothermal reforming. However, these catalysts have drawbacks such as deposition of coke thereon, as pointed out in Int. J. Hydrogen Energy Vol. 8, p539-548 and Hydrogen Energy Progress 4, Vol. 1, p33-45. Thus, autothermal reforming by use of methane as a starting material has been the predominant object of investigation, because the amount of coke deposited on a catalyst is relatively low. Japanese Patent Application Laid-Open (kokai) Nos. 06-256001 and 06-279001 disclose research on production of a synthesis gas through reforming by use of oxygen and steam transformed from methanol by use of a catalyst such as a copper catalyst.
In addition to reactions per se, reactors which can balance heat have been investigated (Journal of Power Sources 61 (1996) p113-124; Hydrocarbon Processing, March 1994, p39-46; and Japanese Patent Application Laid-Open (kokai) No. 07-057756).
Meanwhile, in recent years, carbon dioxide has drawn attention as a substance contributing to global warming. Therefore, in order to fix carbon dioxide and find a use therefor, there has been investigated a method for reforming hydrocarbon by use of carbon dioxide so as to produce a synthesis gas and converting the synthesis gas to products such as methanol, synthetic gasoline, and ethers. Since a number of natural gas fields contain carbon dioxide, there has been investigated a technique for reforming hydrocarbon by use of carbon dioxide as a useful source without isolation from natural gas. However, the technique is not sufficiently developed and thus far has not been brought into practice.
For example, in Nature Vol. 352, Jul. 18, 1991, A. T. Aschroft et al. evaluate catalytic activity of catalysts comprising an alumina carrier carrying Ni, Pd, Ru, Rh, or Ir. Although the Ir catalyst exhibits superior relative catalytic activity, the activity is still insufficient for practical use. Disadvantageous deposition of coke on a catalyst is also pointed out.
In Appl. Catal. 61, 293 (1990), J. T. Lichardson et al. evaluate a ruthenium-on-alumina catalyst and a rhodium-on-alumina catalyst and conclude that deposition of coke is greater on the ruthenium-on-alumina catalyst than on the rhodium-on-alumina catalyst.
Furthermore, Japanese Patent Application Laid-Open (kokai) Nos. 08-175805, 08-259203, 09-075728, and 08-231204 disclose application of a catalyst carrying a Group VIII metal to a process such as reforming of hydrocarbon by use of carbon dioxide.
In addition, Japanese Patent Application Laid-Open (kokai) Nos. 08-196907, 09-029097, and 09-029098 disclose steam reforming of hydrocarbon by use of a catalyst comprising an alumina carrier carrying a metal such as zirconium or ruthenium.
In view of the foregoing, an object of the present invention is to provide a high-performance catalyst for autothermal reforming. Another object of the present invention is to provide a simple and practical method for producing an autothermal reforming catalyst. Still another object of the present invention is to provide a method for producing hydrogen or a synthesis gas through autothermal reforming making use of the above catalyst.
Moreover, yet another object of the present invention is to provide a catalyst for effectively reforming hydrocarbon by use of carbon dioxide. Another object of the present invention is to provide a simple and practical method for producing a catalyst employed in reforming by use of carbon dioxide. Still another object of the present invention is to provide a method for reforming hydrocarbon by use of carbon dioxide and the above catalyst. Yet another object of the present invention is to provide a method for reforming natural gas by use of the above catalyst. Yet another object of the present invention is to provide a method for reforming hydrocarbon or natural gas by use of a mixture of carbon dioxide and steam and the above catalyst. Yet another object of the present invention is to provide a method for reforming natural gas by use of the above catalyst for reforming hydrocarbon. Yet another object of the present invention is to provide a method for reforming hydrocarbon or natural gas by use of a mixture of carbon dioxide and steam and the above catalyst for reforming hydrocarbon.
The present inventors have conducted earnest studies to solve the above-described problems, and have found that a ruthenium-zirconium catalyst, i.e., a ruthenium-on-zirconia catalyst or a ruthenium-zirconium-on-alumina catalyst, is suitable for autothermal reforming as well as for reforming of hydrocarbon by use of carbon dioxide. The present invention was accomplished based on this finding.
Accordingly, in a first aspect of the present invention, there is provided an autothermal reforming catalyst comprising a zirconia carrier carrying ruthenium.
In a second aspect of the present invention, there is provided an autothermal reforming catalyst comprising an inorganic oxide carrier carrying zirconium and ruthenium.
Preferably, in the first and second aspects of the invention, the catalyst contains ruthenium in an amount of 0.05-20 wt. %. Preferably, in the second aspect of the invention, the catalyst contains zirconium in an amount of 0.05-20 wt. % as reduced to ZrO2.
Preferably, in the first and second aspects of the invention, the catalyst further contains cobalt and/or magnesium, with the preferable cobalt content being 0.01-30 based on atomic ratio of cobalt to ruthenium or the magnesium content being 0.5-20 wt. % as reduced to MgO.
Preferably, in the second aspect of the invention, the inorganic oxide carrier is formed of alumina, more preferably xcex1 alumina or xcex3-alumina.
In a third aspect of the present invention, there is provided a method for producing the autothermal reforming catalyst according to the first aspect of the invention, comprising incorporating a solution containing ruthenium, a solution containing ruthenium and cobalt, or a solution containing ruthenium, cobalt and magnesium into a zirconia carrier and then drying and calcining the carrier.
In a fourth aspect of the present invention, there is provided a method for producing the autothermal reforming catalyst according to the second aspect of the invention, comprising incorporating a solution containing zirconium and ruthenium, a solution containing zirconium, ruthenium, and cobalt, or a solution containing zirconium, ruthenium, cobalt, and magnesium into an inorganic oxide carrier and then drying and calcining the carrier.
In a fifth aspect of the present invention, there is provided a method for producing hydrogen or a synthesis gas by use of the above autothermal reforming catalyst.
Preferably, in the fifth aspect of the invention, a starting material for producing hydrogen or a synthesis gas is a hydrocarbon such as methane, liquefied petroleum gas, naphtha, kerosene, or gas oil; methanol; ethanol; or dimethyl ether.
Preferably, in the fifth aspect of the invention, a reforming gas comprises a mixture of oxygen, steam, and carbon dioxide.
In a sixth aspect of the present invention, there is provided a catalyst for reforming hydrocarbon by use of carbon dioxide comprising a zirconia carrier carrying ruthenium.
In a seventh aspect of the present invention, there is provided a catalyst for reforming hydrocarbon by use of carbon dioxide comprising an inorganic oxide carrier carrying zirconium and ruthenium.
Preferably, in the sixth and seventh aspects of the invention, the catalyst contains ruthenium in an amount of 0.05-20 wt. %. Preferably in the seventh aspect of the invention, the catalyst contains zirconium in an amount of 0.05-20 wt. % as ZrO2.
Preferably, in the sixth and seventh aspects of the invention, the catalyst contains cobalt and/or magnesium, with the preferable cobalt content being 0.01-30 based on the atomic ratio of cobalt to ruthenium and the magnesium content being 0.5-20 wt. % as reduced to MgO.
Preferably, in the seventh aspect of the invention, the inorganic oxide carrier is formed of alumina, more preferably xcex1-alumina or xcex3-alumina.
In an eighth aspect of the present invention, there is provided a method for producing the catalyst for reforming hydrocarbon by use of carbon dioxide according to the sixth aspect, comprising incorporating a solution containing ruthenium, a solution containing ruthenium and cobalt, or a solution containing ruthenium, cobalt and magnesium into a zirconia carrier and then drying and calcining the carrier.
In a ninth aspect of the present invention, there is provided a method for producing the catalyst for reforming hydrocarbon by use of carbon dioxide according to the seventh aspect, comprising incorporating a solution containing zirconium, a solution containing zirconium and ruthenium, a solution containing zirconium, ruthenium, and cobalt, or a solution containing zirconium, ruthenium, cobalt, and magnesium into an inorganic oxide carrier and then drying and calcining the carrier.
In a tenth aspect of the present invention, there is provided a method for reforming hydrocarbon by use of carbon dioxide and the above catalyst for reforming hydrocarbon.
In an eleventh aspect of the present invention, there is provided a method for reforming natural gas by use of the above catalyst for reforming hydrocarbon.
In a twelfth aspect of the present invention, there is provided a method for reforming hydrocarbon or natural gas by use of a mixture of carbon dioxide and steam and the above catalyst for reforming hydrocarbon.